A geological surface that separates younger overlying sedimentary strata from eroded igneous or metamorphic rocks and represents a large gap in the geologic record.

分隔较年轻的上覆沉积地层与火成岩或变质岩的侵蚀面的地质界面，在地质记录上代表一个大的间断。

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The new date for the impact (66, 038, 000 years ago) narrows what's been dubbed the 'three metre gap' in the geological record between the demise of the dinosaurs and the asteroid impact to just 18, 000 years.

BBC: Keeping up with the Jinzhousauruses

The question is one of the most hotly contested in palaeontology and revolves around an apparent gap in the fossil record immediately prior to the K-T boundary - the distinct layer of geological sediments separating the Cretaceous and Tertiary periods, and associated with a massive asteroid impact and global extinction event.

BBC: Closing the 'three metre gap'